Vacuum tube system



H. H. GEFFCKEN ET AL 2,058,011

VACUUM'TUBE SYSTEM Filed July 3. 1930 //2 van Zom Heinrich H Gc-Ffiken Hams XE. Ric/2hr Patented Oct. 20, 1936 UNITED STATES PATENT OFFICE zig, Germany,

assignors, by

mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application July 3, 1930, Serial No. 465,728 In Germany July 5, 1929 3 Claims.

This application relates to electron tube circuits and more particularly to circuits directly operated from an alternating current supply source.

An object of the invention is to provide an electron tube control circuit which is simple in construction and economical in operation.

Another object of the invention is to provide an electron tube control circuit, particularly adapted for photo-electric control work in which alternating operating current is used, without impairing the efliciency and reliability of operation.

A further object of the invention consists in providing an electron tube control circuit, supplied from an alternating current operating source which is as easily and as efficiently operated as in the case of direct current operation.

A more specific object of the invention is to provide means in connection with an electron tube control circuit operated by alternating supply current, to suppress the reaction of the variations of the supply current upon the stability of the controlling action.

These and further objects as well as aspects of the invention will become more apparent by the following description taken with reference to the accompanying drawing, illustrating one form of embodiment of the invention. It is understood, however, that Various modifications may be made, coming within the spirit and scope of the invention as comprised by the appended claims.

For economical reasons it is preferable in many instances to operate amplifiers, especially when intended for controlling mechanical relays, directly from an alternating current source. There are, however, difficulties, if the grid voltage of the electron tube is controlled across a high ohmic resistance, such as is usually the case in the amplification of photo-electric currents. It is found that by directly connecting the tube to an alternating current source, the rest potential of the grid, i. e. the biasing potential, when no input signals are applied thereto, assumes a different value from what one would expect in the case of direct current operation. If photo-electric control currents are used, it is impossible, under circumstances, to effect a blocking or choking action of the tube or any other appreciable control of the emission current under conditions for which, when using a direct operating current, a control effect is easily obtained.

To state this otherwise, the present application relates to electron tubes and their control circuits adapted particularly for direct operation from an alternating current source.

We have discovered that in such circuit operation with alternating currents, there exist certain serious disadvantages due to the reaction of the variations of the potential on the anode electrode which in turn cause a variation of capacity reaction from the anode to the grid.

As a result, electrons are trapped on the grid in a manner similar to the well known audion effect. Inasmuch as the grid is a substantially free electrode, electrons attracted thereto are trapped and accumulate to form a negative charge, resulting in a choking or blocking of the tube.

We have discovered that this undesired influencing effect of the alternating current supply upon the grid may be counteracted by providing a condenser connected between the grid and the cathode. This condenser, we have further discovered, must however be at least a multiple of the inherent anode grid capacity which is the cause of the blocking action.

It is the object of the present invention to overcome the aforementioned drawback.

According to the invention, a condenser is connected between the grid and cathode of the electron tube. If the capacity of this condenser is large enough, i. e. if it is a multiple of the capacity existing between anode and grid, the above mentioned objectionable effect is substantially avoided. Thus, it is possible to readily eifect a choking action of the tube, even with a very weak input current, as supplied by a photo-electric cell, and to control in this manner a mechanical relay, directly or indirectly connected in the anode circuit. An explanation of this advantageous effect of the condenser, arranged in accordance with the invention, may be seen to reside in the fact that the electrostatic influencing action of the anode upon the grid is decreased or practically suppressed, if a condenser of sufiicient size is used. Thus it is impossible for temporary charges of the grid due to the above influence and action to accumulate due to electrons being attracted from the discharge path towards the grid, thus producing an undesired permanent negative charge or dislocation of the grid potential. This charge or dislocation may assume values as to give rise to disturbing negative or positive grid currents. The potential of the grid, therefore, by virtue of the condenser connected in accordance with the invention, is influenced by input signal currents only, such as by a potentiometer, comprised of a photo-electric cell and a high ohmic resistance in series.

The invention presents special advantages, if the potential of the grid is controlled by an electron emitting device, such as a photo-electric tube. If the electron emitting device is arranged in such a manner as to be connected to the alternating current potential source in opposite sense with regard to the electron tube, i. e. if electrodes of opposite polarity, such as the anode and cathode of the electron tube and the electron emitting device, respectively, are connected to the same pole of the alternating current source, an extremely simple and economical circuit for practical relay control is obtained. By the opposite connection of the electron emitting device, an alternating operation of the electron tube and of the electron emitting device, respectively, takes place.

A circuit in which the invention is embodied, is shown by the appended drawing, illustrating a photo-electric relay control system. The electron tube 2 is directly connected to the alternating current source, indicated at I2 (it is advisable to provide a potentiometer or transformer for properly adjusting the supply voltage). According to the invention a condenser is connected between the grid 2 and cathode 4 of the electron tube 2. The photo-electric tube 6 is connected in opposite sense, with respect to the electron tube 2, to the alternating current source, i. e. the cathode 1 of the photo-electric tube 6 is connected to the same pole of the alternating current source as the anode 8 of the electron tube 2, whereas the anode 9 of the photo-electric cell 6 is connected across the condenser 5 to the same pole of the alternating current source as the cathode 4 of the electron tube 2, as illustrated. The photoelectric circuit, furthermore, includes a safety or ballast resistance ID. The connection in opposite sense of the electron emitting device 6 has the effect that current is flowing during one alternation through the electron tube and during the other alternation through the photo-electric cell, respectively. Thus, the photo-electric currents may build up during the period during which the electron tube carries neither electron, nor grid currents. As soon as the incoming light rays impinge upon the photo-electric cell during the alternation when the cathode l of the photoelectric cell is negative, the grid 3 of the electron tube and the condenser 5 are charged to negative values. Thus, during the succeeding alternation, when the anode 8 of the electron tube 2 becomes positive, the grid 3 has a negative potential relative to the preceding alternation. The condenser 5 prevents the influencing action of the anode upon the grid in such a manner that the grid remains negative and is not carried temporarily into potential regions, where an undesired compensation of the potential displacement produced by the photo-electric control current, may occur due to ionic or electron currents within the tube 2. Thus, the blocking or choking action by the photo-electric currents of the electron tube is readily secured, even if the controlling currents are very weak, and a closed current relay I, connected in the anode current, is readily actuated. It is understood that in place of the electron tube 2 and the relay, further amplifying stages may be arranged for effecting any desired release or control action.

The choking action of the grid 3 of the electron tube 2 may be limited as to its duration in a desired manner by the arrangement of a leak resistance.

The invention, furthermore, presents special advantages in cases where the grid of the electron tube is controlled capacitatively, i. e. for the socalled impulse choking effect consisting in that a choking eifect of shorter or longer duration of the electron tube is effected by applying a temporary positive charge to the grid. In this case, too, by virtue of the condenser 5, the influencing action of the anode potential cannot materially affect the charge produced by the control impulse, and, consequently, the choking action of the tube. In this latter case, it is advisable to make the condenser 5 sufficiently large, in particular, if the choking action of the electron tube is to last over an extended period.

The advantage, in accordance with the invention, of affording a direct operation of the tube from alternating current, besides the increased simplicity of the circuit, further resides in the absence of expensive batteries or battery eliminators. The residual alternating current component in the anode circuit of the electron tube has no disadvantageous effect upon the operation of most of the known types of relays and besides may be suppressed by well known asymmetrical circuits (push-pull arrangements).

We claim:

1. In combination an electron discharge tube having a cathode, an anode, and a grid, a source of grid control potential comprising a uni-directionally conductive device having its cathode con nected to the anode of said tube and its anode connected to the control grid of said tube,

source of alternating current connected to the anode and cathode of said tube, and a condenser connected between the grid and cathode of said tube, the said condenser having acapacity at least twice the grid-to-anode capacity of the said tube.

2. In combination an electron discharge tube having a cathode, an anode, and a grid, a source of grid control potential comprising a uni-directionally conductive photo-electric cell having its cathode connected to the anode of said tube and its anode connected to the control grid of said tube, a source of alternating current connected to the anode and cathode of said tube, and a condenser connected between the grid and cathode of said tube, the said condenser having a capacity at least twice the grid-to-anode capacity of the said tube.

3. In combination an electron discharge tube having a cathode, an anode, and a grid, a source of grid control potential comprising a uni-directionally conductive photo-electric cell, means including a resistor connecting the cathode of said cell to the anode of said tube and means connecting the anode of said cell to the control grid of said tube, a source of alternating current connected to the anode and cathode of said tube, and a condenser connected between the grid and cathode of said tube, the said condenser having a capacity at least twice the grid-to-anode capacity of the said tube.

HEINRICH H. GEFFCKEN. HANS R. RICHTER. 

